For example, a unidirectional cord fabric (see U.S. Pat. No. 3,859,158) is known as the conventional reinforcement sheet, but this fabric is defective in that, since reinforcing yarns arranged in the warp direction are bent by the pressure thereon of wefts, the capacity of the reinforcing yarns is weakened. Moreover, the fabric is defective in that the reinforcing yarns are not tightly bonded to wefts, crossing points between the reinforcing yarns and wefts are liable to shift, and the handling and processability thereof are poor. Moreover, this fabric has a serious defect in that, since the reinforcing yarns are first bonded to one another by a resin, the fabric has no pliability and the fitting of the fabric in a mold at the molding step is difficult.
As the means for overcoming these defects, there has been proposed a soft reinforcement sheet (fabric) comprising a reinforcing thermoplastic yarn (constituting a matrix after thermal shaping) and a reinforcing yarn (see U.S. Pat. No. 3,620,892, British Patent No. 1,228,573 and British Patent No. 1,226,409). Nevertheless, even according to this proposal, since the matrix yarns and reinforcing yarns are woven into a fabric, the reinforcing yarns in the fabric structure are still bent, and the defect that the capacity of the reinforcing yarns is weakened is not overcome.
Japanese Unexamined Patent Publication No. 60-28543 discloses a method in which polyether ether ketone fiber (matrix fiber) yarns and reinforcing fiber yarns are woven or knitted into a woven fabric, knitted fabric or mat. This prior art technique, for example, in connection with a knitted fabric, teaches only a warp-knitted fabric obtained by arranging matrix fiber yarns and reinforcing fiber yarns, alternately one by one, and knitting them with auxiliary yarns such as polyether ether ketone fiber yarns or glass fiber yarns.
Also, in this case, the reinforcing yarns in the structure of the warp-knitted fabric are bent, and therefore, the above problem is not solved.